1. Field of the Invention
The present invention relates generally to automatic transmissions and more specifically to a control arrangement which facilitates engine braking control.
2. Description of the Prior Art
JP-A-2-51657 discloses an automatic transmission which includes a main four speed main gear train and an auxiliary gear train which can be selective switched between high and low gears. In combination, the main and auxiliary gear trains are arranged to produce 5 forward speeds and one reverse. In order to implement the lowest gear of the main gear train, use is made of a first one-way clutch.
The auxiliary transmission includes a clutch, a brake and a second one-way clutch. When the clutch is engaged the planetary gear assumes a directly engaged condition and produces a speed change ratio of 1. When the clutch is released and the brake (if engaged) or the second one-way clutch are placed under load, a reduction gear condition is established.
The above type of main and auxiliary gear train combinations normally suffer from the problem that when a N-D select is made, the one-way clutches of the main and auxiliary gear trains engage one after the other and produce a two stage shock which deteriorates the select feeling.
In order to prevent double shock problem it has been proposed to engage the brake which is arranged in parallel with the one-way clutch of the auxiliary gear train. That is to say, the brake is initially conditioned to an engaged state so that the one-way clutch is prevented from engaging when a N-D select is made and thus reduces the number of shocks to one.
When the above measure of initially engaging the brake of the auxiliary gear train is employed, the main gear train is provided with a forward one-way clutch in addition to the one-way clutch and is arranged to transmit torque from the engine during forward speeds (with over-drive inhibited). This forward one-way clutch is arranged in parallel with an overrunning clutch the transmission can be selectively switched between a condition wherein engine braking is produced and a condition wherein engine braking is not produced. As a result of this, irrespective of the fact that the brake of the auxiliary gear train is engaged transmission can be selectively conditioned to produce engine braking or non-engine braking conditions.
However, when the main gear train is not provided with the additional forward one-way clutch and the brake of the auxiliary gear train is engaged, switching between engine braking and non-engine braking modes is not possible.